The present invention relates, in general, to a nozzle contact device for guiding and clamping of the injection nozzle of an injection unit of an injection molding machine.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
European Patent Application No. EP 0193617 A1 discloses a nozzle contact device having an injection unit mounted to a guide carriage which can be driven by a subjacent screw mechanism as linear drive. The injection unit is articulated by a vertical rotary pin to the guide carriage so as to be able to laterally swing outwardly in relation to the injection axis, for assembly or maintenance works for example. The screw mechanism includes a ball-screw shaft which has one end rotatably but axially immovably supported in bearings which are secured on the fixed platen. The other end of the screw shaft is connected via a coupling with the output shaft of a motor for the rotary drive of the screw shaft. A ball nut rotatably engages the ball-screw shaft and is supported non-rotatably on the support surface for the injection unit. A spring is arranged between the ball nut and a spring plate, which is secured on the support surface for the injection unit. As the ball-screw shaft rotates, the ball nut and thus the injection unit is able to move to and away from the fixed platen. The nozzle contact pressure can be adjusted via the spring constant and the degree of compression that the spring undergoes. This nozzle contact device is disadvantageous because of the asymmetric force introduction into the nozzle tip and thus into the fixed half of the injection mold and from there into the fixed platen. This results in a comparably significant bending moment, causing inclination of the fixed platen and the attached fixed half of the injection mold. As a consequence, the vertical disposition of the nozzle in relation to the sprue bush of the injection mold changes in dependence on the nozzle contact pressure. At higher contact pressures, the nozzle does not snugly fit upon the sprue bush. Thus, the nozzle contact pressure must generally be limited to prevent leakage between the nozzle and the sprue bush.
An attempt to address this problem is disclosed in Japanese Pat. No. JP 9-277306 which describes a nozzle contact device having two ball-screw shafts on a plane with the injection axis on both sides of the injection unit. Such a nozzle contact device has, however, the drawback that both ball nuts must be operated in synchronism to prevent the injection unit from moving out of the injection axis so that a lateral bending moment is ultimately still generated. A further drawback resides in the fact that the assembly and maintenance of the plasticizing cylinder is made difficult as a lateral swing-out motion is not possible via a vertical rotary pin, and a preceding dismantling of at least one ball-screw shaft is required.
U.S. Pat. No. 6,524,095 B1 discloses a nozzle contact device for an injection molding machine, whereby the injection unit is mounted on a guide carriage which can be driven by a screw mechanism as linear drive and to further articulate the injection unit by means of a vertical rotary pin to the guide carriage so as to be able to swing out laterally in relation to the injection axis. The ball screw and the bearing device of the ball-screw shaft, respectively, are fixed onto the fixed platen via a particularly configured connection piece. This connection piece has a horizontal part which is supported by the machine bed on two guide rails on both sides of the centrally disposed ball-screw shaft. The bearing device for the ball-screw shaft is secured below this horizontal part or forms an integral component of this part. Extending from this horizontal part are two vertical webs in parallel relationship to the platen, at a level of the injection axis, and bolted there to the platen. The bolts are disposed on both sides of the injection axis on one plane therewith. The bolted connection is, however, not tight but loose and in a manner that, on one hand, the bores in the webs have a slightly greater diameter than the bolts, and, on the other hand, sleeves are provided which are disposed between the washers of the bolts and the platen in the bores and are slightly longer than the thickness of the webs in this area so that a small gap is defined between the platen and the connection piece. When the nozzle contact pressure is conducted across the sprue bush and the fixed half of the injection mold into the fixed platen, the connection piece can deform and slightly tilt relative to the platen. As the ball screw-shaft is disposed below the plasticizing cylinder, the latter can be laterally swing via a rotary pin. As an alternative to both webs, the connection piece may also include a vertical piece with a ring, wherein the ring surrounds the nozzle through travel opening in the platen. The ring is loosely secured to the fixed platen in a same manner as the two webs.
This type of nozzle contact device has the drawback that the loose connection between the connection piece and the platen is relatively difficult to implement. The gap between the connection piece and the platen as well as the gap between the sleeve and the bore may not be adjusted too small, on one hand, in order to ensure a sufficient tilting of the connection piece; on the other hand, this gap mass may not be adjusted too great. As it is also desirable to locate the bolted connection of the connection piece as close as possible to the nozzle through travel opening, different connection pieces are to be provided for various diameters of the nozzle through travel opening.
It would therefore be desirable and advantageous to provide an improved nozzle contact device to obviate prior art shortcomings and to avoid the introduction of bending moments into the fixed half of the injection mold or into the injection unit.